(a) Field of the Invention
The present invention relates to a positive active material for a rechargeable lithium battery and a method of preparing the same, and more particularly, to a positive active material for a rechargeable lithium battery exhibiting good electrochemical properties and a method of preparing the same.
(b) Description of the Related Art
Rechargeable lithium batteries use a material from or into which lithium ions are intercalated or deintercalated as positive and negative active materials. Rechargeable lithium batteries produce electric energy by an oxidation and reduction reaction during the intercalation and deintercalation of lithium ions.
For the positive active material in the rechargeable lithium battery, chalcogenide compounds into or from which lithium ions are intercalated or deintercalated are generally used. Typical examples include LiCoO2, LiMn2O4, LiMnO2, LiNiO2, or LiNi1-xCoxO2 (0<X<1). LiCoO2 provides good electrical conductivity, a high cell voltage of about 3.7V, good cycle life and safety characteristics, and high discharge capacity of 160 mAh/g, and thus it is widely used. However, it is very expensive and the cost portion of LiCoO2 reaches to 30% of the total manufacturing cost of the battery. Therefore, it is desirable to develop a low cost positive active material to replace LiCoO2.
Manganese-based materials such as LiMn2O4 or LiMnO2 are easy to prepare, cost less than LiCoO2, are environmentally friendly, and have higher cell voltage (3.9V) than that of LiCoO2. However, the manganese-based materials have a low capacity of about 120 mAh/g, which is smaller than that of LiCoO2 by 20%. Thus, with manganese-based materials it is difficult to fabricate high capacity or thin batteries. LiNiO2 is also lower cost than LiCoO2 and has a high charge capacity, but is difficult to produce. LiNi1-xCoxO2 (0<X<1) also has a larger capacity (200 mAh/g) than LiCoO2, but a lower discharge potential, inferior cycle characteristics to LiCoO2, and poor safety characteristics.